1. Field of the Invention
The purpose of the present invention is to provide a charged particle beam device suitable for reducing focus offset, magnification fluctuation and measurement length error in the charged particle beam device caused by charging on a sample.
2. Description of the Related Art
Recently, as semi-conductor devices, particularly, progress, measuring and inspecting technique of a semi-conductor is more and more increasing its importance. A scanning electron microscope represented by a CD-SEM (Critical Dimension-Scanning Electron Microscope) is a device for measuring the pattern formed on a semi-conductor device by scanning an electron beam on a sample and detecting electrons such as secondary electrons or the like emitted from the sample. In such a device, although the condition of the device is required to be appropriately set to carry out highly accurate measurement and inspection, among recent devices, there are samples wherein the charge adheres by irradiation of an electron beam or influence of a semi-conductor process. Insulator samples such as resist, insulating film, low-k material and the like, in particular, are known as the samples to which the charge is liable to adhere.
Following methods are conventionally devised as methods for measurement of a charging potential. In Japanese Unexamined Patent Application Publication (JP-A) No. 7-288096, a method is disclosed wherein an electron beam is converged on a sample, the electron beam is scanned on the sample, a “reflecting electron” signal obtained according to irradiation of the beam is detected by a detector, an amount of variation of the detected signal in a predetermined time is determined, and either of the pressure around the sample, irradiation amount of the electron beam, and the acceleration voltage of the electron beam is controlled based on the amount of variation obtained (conventional technique 1). Also, a controlling method wherein charging is detected and feed-back is applied based on it is disclosed in the U.S. Pat. No. 6,521,891 (conventional technique 2). According to it, an electron beam is scanned on a sample, a secondary electron and a backscattering electron are detected and an image is formed. The image is obtained by varying accelerating energy of the electron beam, and accelerating energy of the electron beam is varied based on the result of analysis of the image, thereby compensation of charging of the sample is pursued. On the other hand, a method is exhibited in the gazette for the JP-A-1-214769 wherein non-contact measuring of a potential of a sample is performed. A metal needle having a sharpened tip, a feed-back circuit for detecting a field emission current or a tunnel current through the metal needle and to apply a voltage to the metal needle so that the current becomes constant, and a circuit for reading out the metal needle voltage are provided (conventional technique 3).    (Patent Document 1) JP-A-7-288096    (Patent Document 2) U.S. Pat. No. 6,521,891    (Patent Document 3) JP-A-1-214769